Active faulting along the western boundary of the Amur plate (territory of Mongolia)

doi:10.13745/j.esf.sf.2021.12.16

Abstract

Abstract:

The spatial position of the western boundary of the Amur plate within the territory of Mongolia is still not clear; active fault tectonics and the stress state of the Earth’s crust along it have been poorly studied. Within three regions along this border—the Hangay-Khentiy tectonic saddle, the Burgut block (Orhon-Tola interfluve) and the Selenga block, which includes the Selenga depression and the Buren-Nuruu uplift, studies of active faults were carried out using space imagery interpretation, relief analysis, geological structural data and reconstruction of tectonic paleostresses from tectonic fracturing and displacement along with fractures data. It is shown that active faults inherit ancient structural heterogeneities of the Paleozoic and Mesozoic ages. The faults do not form a single zone along the plate boundary, but form clusters. Their kinematics depend on the strike: sublatitudinal faults are left-lateral strike-slip faults with an obligatory reverse component; NW-strike faults are reverse faults or thrusts, most often with a right-lateral strike-slip component; submeridional faults are right-lateral strike-slip faults; and NE-strike faults are normal faults. The activation of fault structures localized in the Selenga depression and in the eastern part of the Hangay began in the Pliocene. Revers and strike-slip faults are not conformal to the Pliocene, and often to the Pleistocene relief, which indicates a younger, Late Pleistocene, age of their activation. Reconstructions of the stress-strain state of the last stage of deformation in zones of active faults, using tectonic fracturing and displacements along fractures, indicate the predominance of compression and strike-slip conditions with the N-NE and NE direction of the axis of maximum compression. Only within the Selenga depression is the prevalence of stress tensors of extension and strike-slip types with the NW strike of the axis of minimum compression noted. To the south, a local area with a predominance of the extension regime is located within the Eastern Hangay (Orhon graben). It is concluded that the activation of faults in the central part of Mongolia at the Pleistocene-Holocene stage, as well as modern seismicity, are mainly controlled by additional horizontal compression in the NE direction associated with the process of convergence of Hindustan and Eurasia. An additional factor that allows the implementation of strike-slip deformations in the crust of the study area and explains the divergent movements in the Baikal Rift, as well as the SE movement of the Amur plate, is the impact on the base of the lithosphere of the asthenospheric flow in the SE direction. The boundary between the Amur plate and the Mongolian block in the tectonic structure is expressed fragmentarily and represents the marginal part of the deformation zone covering the whole of Western Mongolia.

Key words: active faults, paleostress state, fault kinematics, far field effects of collision, Amur plate, Mongolia

Vladimir A. SANKOV, Anna V. PARFEEVETS, Andrey I. MIROSHNITCHENKO, Aleksey V. SANKOV, Amgalan BAYASGALAN, Sodnomsambuu DEMBEREL. Active faulting along the western boundary of the Amur plate (territory of Mongolia)[J]. Earth Science Frontiers, 2022, 29(1): 245-265.

Figures/Tables 6

References 54

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